Big Problem!

OK I didnt know where else to post this so i hope someone can help me big time. I have a huge computer problem. Well my friend who has been helping to fix my computer told me something like a main file is missing, this file helps things run and help be ran and stuff like that. Well this is what happens first of all when you first start my computer Aim and Yahoo messanger are supposed to automatically come up, they now do not. These 2 programs do not work at all, nor does all my other main programs i have on my computer such as adobe photoshop and other things. When I open my start menu My programs arent listed ( i have an XP ) and if they are the picture isnt its original picture its like a shortcut kinda picture....Nothing consiting of video will work when on the internet and my sound also does not work, my friend says this is a major major problem and he needs time to think...my computer is like my life ok and if i dont get this fixed I'm going to die so please someone predict what you think is wrong, some sollusions and how to get whats missing back to not being missing so my computer works properly..* cries * please! :dead: